Spiral horn speakers under construction. Part3

•October 16, 2013 • 4 Comments


Hey there,
Long time no post. Been kinda busy these days but I’m fortunately back in the business.

Finally got the cornu’s sanded, puttied, and white lacquered. It’s been quite a pain in the a** but they turned out great!
Getting the baltic birch plywood prepared for lacquering is a tough job. Lacquer reveals each and every small imperfection in the wood, so to get professional results close care had to be taken when sanding and polishing, specially on corners and joints.

Continue Reading…


Spiral horn speakers under construction. Part2

•April 11, 2013 • Leave a Comment


Finally some updates on my SpiralHorns! Received the pair of Fostex FE108EZ and some damping material couple of days ago. I’m new to Hifi full range drivers, and my first impression was that the banana pulp cone looked so thin and fragile!! On the other side, the HP shell diaphragm looked really cool! I couldn’t wait to hear how they sounded, but the front plate was not glued in place yet. For that reason I decided to set up a provisional scenario to get some initial listening impressions of the speakers. This is what I did, and a small preliminary review of my spiralhorns.
Part3 is soon yet to come with the finished speakers and final listening impressions!!

Continue reading…

Marshall 18watt + VVR

•March 14, 2013 • Leave a Comment


Here one of my latest guitar amps. Marshall 18Watt /w VVR. To be honest I hated the original layout of this amp. Placing the phase splitter tube socket between both first stage preamp tubes doesn’t make sense to me, and can lead to several oscillation problems in the tremolo channel if lead dress is not done properly. This amp produces a very specific sound, turn the volume up and you’ll get really good overdriven tones!!

Some time ago I decided to add a VVR to the amp, so this is a small guide on how I installed a variable voltage regulator, and a couple of things to bare in mind.
Before talking about VVR, a couple more images of the amp and some general specs.

Continue reading…

Spiral horn speakers under construction. Part1

•March 8, 2013 • 4 Comments


Some pictures of my current project, a pair of spiral horn wall mounted speakers.

They’re made from 10mm void free baltic birch plywood, and 4mm okume.
Fullrange drivers still to be chosen. Compared to the size of a guitar each speaker is huge!! The good thing is that they won’t occupy too much space in the room, as they are wall mounted and barely 150 mm depth.

Continue reading…

A word on Carbon composite resistors.

•March 5, 2013 • Leave a Comment


I’m quite a big fan of carbon comp resistors, but I know they’re a double edged sword.  This is a small guide to show where I use them, and why.
It goes without saying that there’s no magic inside this type of resistors, their construction and materials lend itself to their specific characteristics.

Continue reading…

6SL7GT + KT66 Guitar Amp Preamp Tube + Choke

•March 3, 2013 • Leave a Comment


Another post with some components I’ll be using in this amp.

Unfortunately, I don’t have various 6SL7GT to swap and see which one works better with the amp. However I got my hands in a couple, a BrownBase  late 50’s Mullard ECC35 ( just be sure the plate voltage doesn’t exceed 300V ), and a black round plates 50’s Brimar 6SL7GT. I expect these to be good quality tubes , but it’s still difficult to tell without having plugged them in an amp. They were sold as tested, but actually test NEW!!!

On the other hand, I’ll be using a 5H choke in the power rail. It’s a Hammond 158Q 5H @ 150mA


6SL7GT + KT66 Guitar Amp Assembled Board

•February 28, 2013 • Leave a Comment


A picture of the assembled board.
Some specs:

– Allen Bradley RCR Carbon comp plate resistors.
– Piher carbon film resistors
– Welwyn & Ohmite Vitreous Enamel power rail resistors.
– Plessey and CornellDubilier capacitors
– Sprague Atom electrolytics
– Charge Dectection Leds in power supply caps (see older post).

As you see it’s a simple little amp. I put special attention in the layout and grounding scheme, will talk about that sometime soon!!